I would like a 4-speed or more automatic. Is my best all around choice a 700R4, or should I consider something else? Currently I have a 396 coupled to a Th400 from the factory What I'm trying to do is have a good low end, but still have a reasonable highway performer. What about an add-on overdrive, like Gearvendors or some such, or just go to an aftermarket transmission, Tremec maybe? Thoughts?